The long-term objectives of the proposed research are to develop more effective and environmentally safe recombinant bacteria for controlling the mosquito vectors of major human diseases including malaria, filariasis, dengue, and the viral encephalitides. These bacteria will be significantly more cost-effective than Bacillus thuringiensis. subsp israelensis (Bti) and Bacillussphaericus (Bs), the two species currently used in operational vector control programs. In addition, they will be much less prone to induce mosquito resistance, which has already developed to B. sphaericus in field populations of Culex mosquitoes in Brazil, China, and India. To support the sustainable use of these new bacteria in vector control programs, novel combinations of insecticidal proteins will used to be evaluate efficacy and resistance management strategies aimed at controlling mosquito species belonging to the most important vector genera, namely, Anopheles, Aedes, and Culex. The development and use of these new recombinants will be enhanced by studies focusing on improving our knowledge of mechanisms underlying the synergism responsible for the high toxicity and capacity of the CytlA protein to delay, avoid, or overcome resistance in vector populations to other bacterial endotoxins. These objectives will be achieved through a comprehensive research program consisting of the following three specific aims: (1)Construction of improved bacterial insecticides based on novel combinations of mosquitocidal endotoxins; (2) Determination of the target spectrum and toxicity of the bacterial recombinants; and (3) Determination of the general mechanism by which CytlA synergizes endotoxins and overcomes resistance. Bacterial insecticides developed through this research should result in improved vector control and disease reduction, with concomitant health benefits accruing from reductions in the use of broad-spectrum synthetic chemical insecticides. Moreover, the insecticidal protein combinations identified to optimize efficacy and resistance management will provide models for engineering field populations of bacteria and algae for vector control, and for resistance management programs for Bt transgenic crops.